Add red lentils to a saucepan with 2 cups of water. Bring to a boil, then simmer for about 10–12 minutes, or until soft and water is mostly absorbed. Drain any excess water and let cool slightly.
In a large bowl, combine the cooked lentils, grated sweet potato, onion, garlic, cumin, paprika, coriander, salt, pepper, and cilantro. Mix until it holds together. Let sit for 5–10 minutes.
Heat a skillet over medium heat with a drizzle of oil. Scoop the mixture and form it into small patties. Cook for 3–4 minutes per side or until golden and crisp. Repeat in batches.
In a blender or food processor, combine avocado, cilantro, garlic, lime juice, yogurt, salt, and a little water. Blend until smooth and creamy.
Serve the patties warm, topped or dipped with the creamy avocado cilantro sauce.
Notes: Allow the mixture to rest for better binding. Adjust seasoning according to taste. For a spicier kick, add chili powder or diced jalapeños. These patties freeze well; store them in an airtight container.